The present invention relates to a unimorph-type ultrasound probe, and in particular, to a unimorph-type ultrasound probe for achieving reduction in a side lobe in a minor axis direction.
Conventionally, in the medical field, an ultrasound diagnostic apparatus using ultrasound images has been put to practical use. Generally, in this type of ultrasound diagnostic apparatus, an ultrasonic beam is transmitted toward the inside of a subject from an ultrasound probe, an ultrasonic echo from the subject is received by the ultrasound probe, and the received signal is electrically processed, thereby generating an ultrasound image.
It is known that, when an ultrasonic beam is transmitted from an ultrasound probe, not only a main lobe having high sound pressure is radiated on a central axis in a transmission direction, but also a side lobe having low sound pressure is radiated in a direction deviated from the central axis. An ultrasonic echo from a reflector positioned on the side lobe is received along with an ultrasonic echo due to the main lobe, which causes a problem in that an ultrasound image becomes unclear.
As a method of reducing a side lobe, a method, called apodization, is generally used. This method is a method in which, instead of applying a uniform voltage to each transducer of a transducer array arranged in a major axis direction as shown in FIG. 9A, by applying a lower voltage to a transducer positioned closer to the end portion of the array as shown in FIG. 9B, the radiation of an ultrasonic beam from the end portion of the array is suppressed to narrow down the ultrasonic beam. By the method, it is possible to reduce a side lobe which is radiated in the direction deviated from the central axis.
In a one-dimensional array in which transducers are arranged in a row in a major axis direction, it is possible to use the apodization with respect to the major axis direction. However, since only one transducer exists in a minor axis direction, it is not possible to reduce a side lobe with respect to the minor axis direction using the apodization.
Accordingly, for example, JP 02-41144 A discloses an ultrasound probe in which a piezoelectric substance constituting each transducer is shaped so as to have a so-called rhombic planar shape of which the width becomes narrower toward the end portion in a minor axis direction, and these shaped piezoelectric substances are arranged in a major axis direction.
By causing the piezoelectric substance to have such a planar shape, in each transducer, an ultrasonic beam which is radiated from the end portion in the minor axis direction is suppressed, and an ultrasonic beam which is narrowed down in the minor axis direction can be formed. With this, it is possible to achieve reduction in a side lobe even in the minor axis direction.
However, it is not easy to shape a bulk piezoelectric substance made of a conventional inorganic material so as to have a rhombic planar shape. Although an attempt to realize a piezoelectric substance having a rhombic planar shape using a dicing saw was made, it was necessary to carry out special cutting in a direction inclined with respect to the arrangement direction of the piezoelectric substances, and a lot of labor, time, and cost were required.